This isn't about the expectation that customers clean off their own tables. This is a simple request that passengers perform a minimal courtesy which benefits the next passengers (and, in turn benefits you when you board an aircraft the next time).
The fact that people even kvetch about being asked to perform the simplest of things is a troubling comment about self-indulgence and self-entitlement at its worst.
To those who are asked and who don't: it is unlikely that you will be shot, jailed or bound to your seat for all eternity. The world will move on.